1. Field of the Invention
The present invention relates to a structure of an engine of a vehicle, particularly of snowmobile.
2. Related Art
In a snowmobile mounted with the water-cooling type engine in a transverse attitude, if the engine has a high full height, a head cover arranged to the engine top portion adversely affects an engine hood, headlight or like disposed further above the engine. In order to obviate such defect, the engine of this type is arranged in an inclined manner in an engine room such as shown in Japanese Patent Laid-open (KOKAI) Publication No. 2002-371847.
Further, the engine head cover of this type is formed with a plug hole for mounting an ignition plug thereto. Water is likely stored in this portion, so that a cylinder head is formed with a drain passage, for example, on an exhaust port side as disclosed in Japanese Patent Laid-open (KOKAI) Publication No. 2000-110660.
However, in the arrangement in which the engine is inclined forward, the front side of the engine hood will take a high position, which leads to an increasing of air resistance. In this meaning, it may be desired to incline the engine rearward. However, in a case where the engine is inclined rearward over some extent, it adversely affects the arrangement of ducts and wiring for an intake system of the engine, and there is a fear of interfering with the engine, a fuel tank and the like. In this meaning, there is a limit for rearward inclination of the engine.
Furthermore, in a case where a drain (drainage) passage is formed on the exhaust port side of the cylinder head, it is difficult to locate a cooling water jacket around the exhaust port. As a result, the exhaust port will be exposed to a high temperature from the engine exhaust gas, which may result in thermal deformation of the surrounding of the exhaust port and the mating portion to the cylinder block.
On the other hand, in a snowmobile mounted with a water-cooling type engine in a transverse attitude, a cooling water outlet is provided at a portion on a power take-out side of the engine and the outlet is covered by a cover provided with a thermostat as disclosed in the above-mentioned Japanese Patent Laid-open (KOKAI) Publication No. 2002-371847.
In such an engine, the cover covering the cooling water outlet projects in a width direction of the engine, which expands the width of the engine structure, which adversely affects an engine hood design.
That is, for example, on the power take-out side of the engine, a clutch is arranged near the engine, and accordingly, it is necessary to take care the arrangement of cooling ducts such as cooling water hose or bypass hose, wirings of water temperature sensor and the like to prevent the clutch from contacting to the ducts or wirings.
Further, a cam-chain is also arranged in the engine on the side opposite to the power take-out side of the engine, and according to such arrangement, it is difficult to form the cooling water outlet and the thermostat on this opposite side.